The towing of large capacity trailers requires rugged and robust lock mechanisms, such as those utilized by so-called “fifth wheel” units on semi tractors. Such locks typically include a depending king pin mounted on the trailer and a wedge receiver mounted on the tractor, having a king pin receiving slot defined in a load bearing plate and a locking mechanism. To connect a trailer to the tractor, the tractor is backed toward the trailer and the king pin rides into the slot and is captured therein by tripping the locking mechanism. See for example, U.S. Pat. No. 5,456,484. These locks are designed to endure the rigors of travel, as well as hitching and unhitching procedures, without compromising the integrity of the lock and introducing the danger of becoming unhitched during over-the-road operation.
Standard fifth wheel locking mechanisms feature a release that is actuated by manually pulling a release bar extending out one side of the fifth wheel unit. Due to the rugged design required of such locks, the pulling force required to release these locks can be quite high. Various factors (age, weather, extended periods of inactivity, etc.) may create a situation where the mechanism will “freeze” in the locked disposition and an operator cannot readily unlock the lock by manual means.
Some fifth wheel units are equipped with a powered mechanism that works independent of the manual release to unlock the fifth wheel, such as disclosed in U.S. Pat. No. 5,456,484. The power provided by these units overcomes many of the factors that would otherwise render a release manually impossible. However, such mechanisms are an integral part of the fifth wheel hitch unit, with components mounted underneath the load bearing plate. Components for such mechanisms tend to be custom made or specialized to stay within the footprint of the fifth wheel hitch unit. Moreover, acquiring the power assist release provided by these fifth wheel hitch units would require replacing the entire fifth wheel unit, rather than the more cost effective retrofitting of the existing fifth wheel hitch unit. A system is desired that avoids the expense of specialized components, and allows retrofitting of existing fifth wheel hitch units with a power assist system that also retains the manual unlock capability.
There are also known large capacity trailers that utilize a second fifth wheel hitch unit on the trailer itself, in addition to the fifth wheel hitch unit of the semi tractor. An example of such trailers is the TITANIUM™ Series of trailers manufactured by Towmaster, Inc. of Litchfield, Minn., the assignee of the present patent application and owner of the noted tradenark. Referring to prior art FIGS. 1 and 2, a detachable gooseneck trailer 10 is portrayed. The trailer 10 is coupled to the tractor in the same manner as noted above. Further, these trailers have a gooseneck 12 that is detachable from a bed 14 in order to provide for the loading of very large vehicles on the bed from the front of the bed 14. Such trailers 10 include a second fifth wheel hitch unit as depicted at 16 of prior art FIG. 2. The fifth wheel hitch unit 16 is mounted to the bed 12. The fifth wheel hitch unit 16 provides for connections between a king pin mounted the gooseneck 12 and the bed 14. The fifth wheel hitch unit 16, in cooperation with other coupling means, couples the gooseneck 12 and the bed 14 as a unit, as depicted in prior art FIG. 1. As can be seen, access to both sides of the fifth wheel hitch unit 16 is somewhat restricted because of the framework of the bed 14, especially when the gooseneck 12 is coupled to the bed 14.
To facilitate release of the locking mechanism 17 of the fifth wheel hitch unit 16, an exemplary locking mechanism 17 (depicted in greater detail in FIGS. 11 and 12, includes a release bar 18 that extends through a support beam or framework 20 of the bed 14. An operator releases the locking mechanism 17 by pulling outward on the release bar 18 beyond the flange 21 of the framework 20. The king pin mounted on the gooseneck 12 is then free to slide forward in the king pin slot 19, thereby disengaging the gooseneck 12 from the bed 14. When the locking mechanism 17 is reset to the locked disposition, the tripping action of the king pin engaging the locking mechanism 17 causes the locking mechanism 17 to shift into the locked disposition automatically. Such action automatically retracts the release bar 18 back under the flange 21 of the framework 20. In this way, the release bar 18 serves as a visual indicator as to the status of the locking mechanism 17: if the release bar 18 is retracted, the operator knows the locking mechanism 17 is in the locked disposition; if the release bar 18 is extended, the operator knows the locking mechanism 17 is in the unlocked disposition.
It is common to utilize a fifth wheel hitch unit 16 for locking the gooseneck 12 to the bed 14. However, spatial constraints of certain trailer designs may preclude the use of existing power assisted fifth wheel units requiring a larger footprint to accommodate the power assist components. Also, many power assist units have manual release bars that are decoupled from the powered actuation train, which eliminates the benefit of a visual indication of the status of the lock. That is, a powered release of the locking mechanism 17 does not serve to extend the release bar 18 relative to the framework 20 of the bed 14, and an operator would have to verify setting of the locking mechanism 17 by other means. Hence, in addition to the desired traits enumerated above, there is a demand for a system that retains the visual indication provided by the manual release bar in a power assisted device and a device that can be selectively manually operated and power assist operated.